cons.saver setgid paranoia: Don't open arbitrary file

[egmontkob]

Is there an existing issue for this?

• I have searched the existing issues

Midnight Commander version and build configuration

4.8.33, git

Operating system

Linux

Is this issue reproducible using the latest version of Midnight Commander?

• I confirm the issue is still reproducible with the latest version of Midnight Commander

How to reproduce

Setgid cons.saver checks that the passed device name is at most 15 bytes and begins with /dev/, and then proceeds and opens it for reading.

This allows one to create a symlink /dev/../tmp/x pointing wherever, and get cons.saver open it for reading.

Of course cons.saver will immediately check if it's indeed a terminal device and quit otherwise. Still, I'm not happy this amount of slack in a setgid tool.

Let's check that the passed string strictly matches the pattern /dev/tty[0-9]+.

Or rather: Maybe just pass the plain number as parameter, and let cons.saver prepend /dev/tty and /dev/vcsa.

While at it, we could remove the devfs-specific code, devfs has been obsoleted and replaced by udev in Linux 2.6 or so.

Expected behavior

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Actual behavior

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Additional context

No response